EP1148837B1

EP1148837B1 - System for controlling thermal therapy

Info

Publication number: EP1148837B1
Application number: EP99965224A
Authority: EP
Inventors: Eric N. Rudie; Jonathan L. Flachman; James E. Burgett; Thayne R. Larson
Original assignee: Urologix Inc
Current assignee: Urologix Inc
Priority date: 1998-12-11
Filing date: 1999-12-10
Publication date: 2012-09-26
Anticipated expiration: 2019-12-10
Also published as: WO2000033767A1; AU762862B2; US6490488B1; EP1148837A1; JP2002531218A; AU3118800A; EP1148837A4; US6122551A; CA2354587A1

Description

BACKGROUND OF THE INVENTION

The present invention relates to a thermal therapy system for treating tissue such as the prostate with enhanced treatment effectiveness and minimal treatment time.
The prostate gland is a complex, chestnut-shaped organ which encircles the urethra immediately below the bladder. Nearly one third of the prostate tissue anterior to the urethra consists of fibromuscular tissue that is anatomically and functionally related to the urethra and the bladder. The remaining two thirds of the prostate is generally posterior to the urethra and is comprised of glandular tissue. The portion of the urethra extending through the prostate (i.e., the prostatic urethra) includes a proximal segment, which communicates with the bladder, and a distal segment, which extends at an angle relative to the proximal segment by the verumontanum.
Although a relatively small organ, the prostate is the most frequently diseased of all internal organs and is often the site of a common affliction among older men, benign prostatic hyperplasia (BPH), as well as a more serious affliction, cancer. BPH is a nonmalignant, bilateral expansion of prostate tissue occurring mainly in the transition zone of the prostate adjacent to the proximal segment of the prostatic urethra. As this tissue grows in volume, it encroaches on the urethra extending into the region of the bladder neck at the base of the bladder. Left untreated, BPH causes obstruction of the urethra which usually results in increased urinary frequency, urgency; incontinence, nocturia and slow or interrupted urinary stream. BPH may also result in more severe complications, such as urinary tract infection, acute urinary retention, hydronephrosis and uraemia.
Benign prostatic hyperplasia (BPH) may be treated using transurethral thermal therapy as described in further detail in U.S. Patent 5,620,480 entitled METHOD FOR TREATING BENIGN PROSTATIC HYPERPLASIA WITH THERMAL THERAPY and in U.S. Patent 5,575,811 entitled BENIGN PROSTATIC HYPERPLASIA TREATMENT CATHETER WITH URETHRAL COOLING, During transurethral thermal therapy, the transition zone of the prostate is heated to necrose the tumorous tissue that encroaches on the urethra. Transurethral thermal therapy is administered by use of a microwave antenna-containing catheter which includes a multi-lumen shaft. The catheter is positioned in the urethra with the microwave antenna located adjacent to the hyperplastic prostatic tissue. Energization of the microwave antenna causes the antenna to emit electromagnetic energy which heats tissue within the prostate. A cooling fluid is circulated through the catheter to preserve tissue such as the urethral wall between the microwave antenna and the target tissue of the prostate. US 5 755 754 discloses the system of the preamble of appended claim 1.
The primary goal of transurethral thermal therapy is to necrose prostate tissue while preserving adjacent healthy tissue. It is also preferable to achieve this goal in as short of a time as is possible, consistent with the patient's level of tolerance and comfort. In addition, it is important that the rectum be preserved from unduly high temperatures, since it is susceptible to thermal damage. There is an ongoing need in the art for a method of controlling thermal therapy that reduces treatment time and enhances effectiveness consistent with all of these parameters.

SUMMARY OF THE INVENTION

The present invention is a thermal therapy system for treating tissue with heat from an adjacent body cavity, such as treating a prostate with heat delivered from a urethra as defined in appended claim 1. An applicator is insertable into the body cavity, and includes a microwave antenna and at least one cooling fluid chamber for circulating a coolant between the microwave antenna and a wall of a body cavity in which the applicator is capable of insertion. A microwave generator is operable to energize the microwave antenna in the applicator, and a coolant temperature controller is operable to control a temperature of the coolant circulating between the microwave antenna and the wall of the body cavity. A control system selectively operates the microwave generator and the coolant temperature controller to adjust the temperature of the coolant according to a predetermined coolant temperature profile, continually adjust coolant temperature based on therapy parameters, and maintain the applicator at a temperature corresponding to a predetermined applicator temperature profile by controlling the temperature of the coolant in coordination with a power level provided to the microwave antenna. In one exemplary embodiment, where the targeted tissue region is the prostate adjacent the urethra, rectal temperature is monitored and, upon sensing a predetermined rectal temperature profile, coolant temperature is adjusted. Coolant temperature may also be adjusted based on patient comfort indicators. The applicator is maintained at a temperature corresponding to a predetermined applicator temperature profile by adjusting a power level provided to the microwave antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section view of a male pelvic region showing the urinary organs affected by benign prostatic hyperplasia.
FIG. 2 is an enlarged view of the male pelvic region of FIG. 1 showing a urethral catheter positioned in the prostatic region.
FIG. 3 is a cross-sectional view of a first exemplary urethral catheter.
FIG. 4 is a cross-sectional view of a second exemplary urethral catheter.
FIG. 5 is a block diagram of an exemplary transurethral microwave thermal therapy control system.
FIGS. 6A and 6B are graphs illustrating basic tissue temperature/depth curves at different power levels and coolant temperatures during thermal therapy.
FIGS. 7A and 7B are block diagrams illustrating the thermal therapy control methods according to two embodiments of the present invention.
FIG. 8A is a graph illustrating temperatures achieved during a thermal therapy treatment session according to one variation of the control method of the present invention.
FIG. 8B is a graph illustrating temperatures achieved during a thermal therapy treatment session according to a second variation of the control method of the present invention. -

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a vertical sectional view of a male pelvic region showing the effect benign prostatic hyperplasia (BPH) has on the urinary organs. Urethra 10 is a duct leading from bladder 12, through prostate 14 and out orifice 16 of penis end 18. Benign tumorous tissue growth within prostate 14 around urethra 10 causes constriction 20 of urethra 10, which interrupts the flow of urine from neck 22 of bladder 12 to orifice 16. The tumorous tissue of prostate 14 which encroaches urethra 10 and causes constriction 20 can be effectively removed by heating and necrosing the encroaching tumorous tissue. Ideally, periurethral tumorous tissue of prostate 14 anterior and lateral to urethra 10 is heated and necrosed to avoid unnecessary and undesirous damage to urethra 10 and to adjacent healthy tissues, such as ejaculatory duct 24 and rectum 26. A selective heating of benign tumorous tissue of prostate 14 (transurethral thermal therapy) may be achieved by utilizing a microwave antenna-containing catheter such as is shown in U.S. Patent 5,620,480 or U.S. Patent 5,575,811 .
FIG. 2 shows an enlarged view of the male pelvic region of FIG. 1 with a catheter 27 simplistically shown properly positioned within urethra 10. While the particular structure of catheter 27 may vary and a number of lumens may be provided therein, catheter 27 typically includes transmission line 28 connected to microwave antenna 30 for emitting microwave energy to prostate 14. Cooling fluid is circulated along paths 32 between microwave antenna 30 and the walls 36 of urethra 10, so as to conductively cool the tissue of urethra 10 when microwave antenna 30 is energized to radiate microwave energy to prostate 14. Catheter 27 may be secured within urethra 10 by retention balloon 34 located in bladder 12, for example. The temperature of the urethra may be detected by providing a temperature sensor on catheter 27 contacting urethral walls 36. In addition, the temperature of rectum 26 may be detected by inflating a balloon or providing another type of device in rectum 26 that includes a temperature sensor in contact with the rectal wall, such as is disclosed in U.S. Patent 5,792,070 entitled RECTAL THERMOSENSING UNIT, (particular reference being made to FIG. 1, which illustrates an inflated rectal thermosensing unit carrying a temperature sensor, and the accompanying description at column 3, line 24 - column 5, line 42).
FIG. 3 is a cross-sectional view of a first exemplary urethral catheter 27a. As shown in FIG 3, urethral catheter 27a includes ridges 38, sleeve 40, outer thermal sensing lumen 41, apertures 42A and 42B, chamber 43, microwave antenna lumen 44, urine drainage lumen 46, coolant fluid return lumen 48, inflation lumen 52, inner thermal sensing lumen 54, fluid channels 58 and 60, antenna jacket 61, and coolant fluid supply shaft 63. Outer thermal sensing lumen 41 and inner thermal sensing lumen 54 contain a thermal sensor which monitors the temperature of urethra 10 during therapy. Antenna jacket 61 securely contains a microwave antenna (not shown in FIG. 3) during therapy.
Fluid channel 60 provides a supply path for the cooling fluid between coolant fluid supply shaft 63 and chamber 43 while fluid channel 58 provides a return path for the cooling fluid between chamber 43 and lumen 48. The cooling fluid is circulated from coolant fluid supply shaft 63 into chamber 43 via aperture 42B and fluid channel 60. The cooling fluid fills chamber 43 defined by catheter shaft 33 and PET sleeve 40. The cooling fluid returns to catheter shaft 33 through coolant fluid return lumen 48 via aperture 42A and fluid channel 58.
FIG. 4 is a cross-sectional view of a second exemplary urethral catheter 27b. Cooling fluid intake lumens 74A, 74B are positioned circumjacent first side 78 of shaft 31 and antenna lumen 68. Cooling fluid intake lumens 74A and 74B extend from the distal shaft end to the proximal shaft end. Intake lumens 74A and 74B are relatively narrow in cross-section and have a relatively small cross-sectional surface area. Water contained within intake lumens 74A and 74B performs two essential functions. First, water contained within lumens 74A and 74B absorbs some of the microwave energy emitted by an antenna contained in antenna lumen 68. This assists in controlling the volume of tissue adjacent first side 78 of shaft 31 that is heated above about 45° C. Second, water within lumens 74A and 74B absorbs heat energy generated by the microwave energy from adjacent tissues (i.e., urethra 10) via thermal conduction. This prevents urethra 10 adjacent first side 78 from being overheated and damaged when the antenna is energized.
Cooling fluid exhaust lumens 76A and 76B are circumjacent second side 82 and antenna lumen 68. Like intake lumens 74A and 74B, exhaust lumens 76A and 76B extend from the shaft distal end to the shaft proximal end. Exhaust lumens 76A and 76B are wider in cross-section than intake lumens 74A and 74B, and have a cross-sectional area greater than the cross-sectional area of intake lumens 74A and 74B. Water within exhaust lumens 76A, 76B is therefore capable of absorbing a greater amount of microwave energy when the antenna is energized. As a result, for a given power output from the microwave generating source, the temperature of tissue adjacent second side 82 will remain below about 45° C. Water within exhaust lumens 76A, 76B also absorbs heat energy from adjacent tissue (i.e., urethra 10) when the antenna is energized, which prevents urethra 10 adjacent second side 82 from being overheated and damaged when the antenna is energized.
FIG. 5 is a block diagram of an exemplary transurethral microwave thermal therapy system 92, with which urethral catheter 27 is used. System 92 includes cooling system 86, microwave generating source 84, user interface 94, real time controller (RTC) 96, directional coupler 100, thermometry sensors 102 and 104, coolant pressure sensor 114, balloon inflation device 110, and urine collection container 112.
As shown in FIG. 5, control of microwave generating source 84 and cooling system 86 is effected by RTC 96, which is in turn controlled by user interface 94. In one preferred embodiment, user interface 94 is an IBM compatible machine containing two hard drives for data storage: one for backup, and one for normal operation of system 92. User interface 94 communicates with RTC 96, which is responsible for closed-loop feedback to run system 92. RTC 96 has direct closed-loop control of microwave power from microwave generating source 84, and coolant flow and coolant temperature of cooling system 86. The closed-loop feedback of RTC 96 tracks out variations in gain, drift and cable losses inherent in microwave generating source 84. RTC 96 also tracks the variability in pump output and refrigeration system efficiency of cooling system 86. In addition to monitoring microwave generation source 84 and cooling system 86, RTC 96 also monitors and controls several channels of thermometry via inputs from thermometry unit 98. Cooling system thermometry 98A measures the coolant and chiller temperatures based upon signals from cooling temperature sensor 102 and 104 and a chiller temperature sensor (not shown) of cooling system 86. Urethral thermometry 98B measures urethral temperature based upon signals from a temperature sensor within catheter 27. Rectal thermometry 98C measures rectal temperature based upon signals received from a sensor (not shown) within rectal probe 108.
RTC 96 transmits closed-loop feedback to user interface 94, which processes the input and transmits corrections and instructions back to RTC 96. RTC 96 interprets the instructions given to it by process control language received from user interface 94 and executes the instructions in real time. Corrections from user interface 94 are made to maintain a desired thermal profile throughout the transurethral thermal therapy. In addition, system 92 includes a hardware fail-safe circuit which shuts down system 92 should any parameter fall outside a given range of values.
FIGS. 6A and 6B are graphs illustrating basic tissue temperature/depth curves at different power levels and coolant temperatures during thermal therapy, and demonstrating the basic principles of the present invention. Particularity, FIG. 6A illustrates tissue temperature/depth curves for a treatment session where catheter temperature is held at a predetermined value (such as 40°C), and FIG. 6B illustrates tissue temperature/depth curves for a treatment session where a certain depth of tissue around the catheter is held at a predetermined value (such as 40°C). The vertical axes of FIGS. 6A and 6B represent the temperature of tissue, and the horizontal axes represent the depth from the catheter/urethra of that tissue. Therefore, a depth of zero represents the urethral wall.
Each of the curves shown in FIG. 6A represents a different coolant temperature and microwave power condition, with the constant criteria for each curve being that the temperature of the catheter (at depth=0) is maintained at a steady-state temperature such as 40°C. Curve 120 represents a situation where microwave power is zero and coolant temperature is equal to the steady-state catheter temperature (e.g., 40°C), curve 122 represents a situation where the microwave power is high and coolant temperature is at a minimum (such as 8°C, for illustrative purposes) and the curves between curve 120 and curve 122 represent situations where the microwave power is between zero and the high value, and the coolant temperature is between the steady-state catheter temperature (e.g., 40°C) and (the minimum coolant temperature (e.g., 8°C). Each curve is labeled according to the relative coolant temperature (t_c) and power level (p), so that curve 120 represents the highest coolant temperature (t_c1) and the lowest power (p₇) and curve 122 represents the lowest coolant temperature (t_c7) and the highest power level (p₁), wherein each curve is predicated on the condition that catheter temperature is maintained at a steady-state temperature such as 40°C. The particular values of the minimum coolant temperature and corresponding power level depend on -the structure and characteristics of the treatment catheter employed, and it should be understood that the exemplary values provided herein refer only to one particular catheter structure; othervalues are appropriate for different catheter structures, while still practicing the present invention. As can be seen from the curves shown in FIG. 6A, when the catheter temperature is maintained at a steady-state temperature such as 40°C, decreased coolant temperature results in deeper heating of tissue in the prostate due to the increased power level required to maintain the catheter at the steady-state temperature. This may result in a greater depth of necrosis caused by heating the tissue above a particular threshold temperature.
Each of the curves shown in FIG. 6B also represent a different coolant temperature and microwave power condition, with the constant criteria for each curve being that the temperature of tissue at a depth of interest, defining a zone of protection from the outer surface of the catheter to that tissue depth (such as 1 millimeter, for example), is maintained at a steady-state temperature such as 40°C. Curve 124 represents a situation where microwave power is slightly greater than zero and coolant temperature is equal to a temperature slightly greater than the steady-state tissue temperature (e.g., 40°C), which is slightly different from the power and coolant temperature shown in curve 120 (FIG. 6A) where the catheter rather than a depth of tissue was maintained at a steady-state temperature such as 40°C. Curve 126 represents a situation where the microwave power is high and coolant temperature is at a minimum (such as 8°C, for illustrative purposes) and the curves between curve 124 and curve 126 represent situations where the microwave power is between zero, and the high value, and the coolant temperature is between the steady-state tissue temperature (e.g., 40°C) and the minimum coolant temperature (e.g., 8°C). Each curve is labeled according to the relative coolant temperature (t_c) and power level (p), so that curve 124 represents the highest coolant temperature (t_c1) and the lowest power (p₇) and curve 126 represents the lowest coolant temperature (t_c7) and the highest power level (p₁), wherein each curve is predicated on the condition that tissue temperature is maintained at a steady-state temperature such as 40°C. The particular values of the minimum coolant temperature and corresponding power level depend on the structure and characteristics of the treatment catheter employed, and it should be understood that the exemplary values provided herein refer only to one particular catheter structure; other values are appropriate for different catheter structures, while still practicing the present invention. As can be seen from the curves shown in FIG. 6b, when the tissue temperature at a depth of interest is maintained at a steady-state temperature such as 40°C, decreased coolant temperature results in deeper heating of tissue in the prostate due to the increased power level required to maintain the tissue at the steady-state temperature. This may result in a greater depth of necrosis caused by heating the prostate tissue above a particular threshold temperature.
In the thermal therapy curves depicted in FIGS. 6A and 6B, if coolant temperature is continually decreased and microwave power is correspondingly continually increased to maintain the catheter or tissue temperature at the steady-state temperature or at a set point temperature while initially ramping up the catheter/tissue temperature, temperatures at the depth of the rectum may become unacceptably high. In other words, high temperatures are achieved at too great of a depth from the catheter/urethra. Therefore, in a preferred method of controlling thermal therapy, rectal temperature is utilized as a parameter for controlling the coolant temperature (and the catheter/tissue temperature set point, temporarily) to enable optimal therapy without thermally damaging the tissue of the rectum.
FIG. 7A is a block diagram illustrating a complete thermal therapy control method according to a first embodiment of the present invention, utilizing the principles and parameters discussed above with respect to FIG. 6A. To initialize the therapy, a physician enters inputs related to catheter temperature at block 130a and inputs related to coolant temperature at block 132. Specifically, a physician enters an initial ramp rate of catheter temperature (that is, how quickly and in what manner the catheter temperature is to increase from its initial temperature of approximately body temperature (37°C) to its final, steady-state temperature) and a steady-state catheter temperature. In addition, the physician enters a coolant temperature ramp rate (that is, how quickly and in what manner the coolant temperature is to decrease from its initial temperature to a targeted final temperature), an initial coolant temperature and a steady-state coolant temperature. The catheter temperature ramp rate and the coolant temperature ramp rate may comprise a ramping function, such that cathetertemperature and/or coolant temperature increases or decreases exponentially, linearly, or according to some other function that enhances the effectiveness of the therapy consistent with patient comfort concerns. The exact value and degree of physician contribution of these inputs will depend on experimental results of therapy in particular patients, and are set consistent with a desired patient comfort level. The actual format of physician input may also be simplified by an appropriate software program or other means, so that the physician enters only minimal data and the program calculates the therapy inputs from the data entered by the physician. The physician inputs are further explained graphically below with respect to FIGS. 8A and 8B.
From the catheter temperature inputs entered at block 130, a catheter temperature profile is established at block 138. The catheter temperature profile represents a desired characteristic of catheter temperature at a particular time in the thermal therapy session, which may of course be adjusted by other parameters such as rectal temperature and patient comfort during the course of the therapy, as noted below. From the coolant temperature inputs entered at block 132. a coolant temperature profile is established at block 134. The coolant temperature profile also represents a desired characteristic of coolant temperature at a particular time in the thermal therapy session, which again may be adjusted by other parameters such as rectal temperature and patient comfort during the course of the therapy, as noted below.
The catheter temperature profile signal is passed on to adder/subtractor 136, which passes a modified cathetertemperature set point signal on to Microwave Power Control block 140, which in one preferred embodiment is implemented as a proportional/integrat/differential (PID) control loop. PID control loops are algorithms known in the art for controlling a process to achieve a desired output level. The power delivered to the microwave antenna 30 (FIG. 2) energizes the antenna to radiate electromagnetic energy, resulting in elevation of prostate tissue temperature as represented by block 142. Power delivered to the microwave antenna is continually adjusted to ensure that the catheter remains at the modified catheter temperature set point; therefore, Microwave Power Control block 140 is responsive to the measured catheter temperature at block 148 to adjust microwave power accordingly.
Elevation of prostate tissue temperature at block 142 causes a biological response in the tissue, which is represented by block 144. One response is increased blood perfusion in the tissue, which tends to conduct heat away from a particular portion of tissue and reduce the heating effect on the tissue. Also, when electromagnetic energy is delivered to elevate the temperature of prostate tissue, the temperature of the rectum may also be increased. Rectal temperatures are therefore monitored during thermal therapy to ensure that the rectum is not thermally damaged by excessively high temperatures; the measured rectal temperature is represented by block 146. If rectal temperature reaches a predetermined threshold, steps must be taken to reduce the temperature of the rectum so that it may be preserved. In an ideal situation, coolant temperature would be immediately increased (with microwave power correspondingly decreased to maintain catheter temperature at the desired set point) in response to high rectal temperatures. However, in actuality, it may not be possible to instantaneously change the temperature of the coolant. Therefore, to safely ensure preservation of the rectum, according to one preferred embodiment of the present invention, the catheter temperature is initially reduced in response to high rectal temperatures by a catheter temperature modifier represented at block 150. The catheter temperature modifier is subtracted by adder/subtractor 136 from the desired catheter temperature provided by the catheter temperature profile to yield a modified catheter temperature set point, which is input to Microwave Power Control block 140. By reducing the catheter temperature set point immediately, with all other parameters remaining the same, the microwave power will be reduced and tissue temperatures will immediately decrease. For increasingly higher rectal temperatures, the catheter temperature set point is decreased by a greater amount. In addition, a Coolant Temperature Control block 152 implements a PID control loop, for example, to determine an increased temperature of the coolant. Comparator block 154 outputs the higher of the coolant temperature provided by the coolant temperature profile at block 134 and the coolant temperature provided by Coolant Temperature Control block 152. In other words, the desired coolant temperature is determined by the coolant temperature profile at block 134 unless an excessively high rectal temperature causes a higher coolant temperature to be determined by Coolant Temperature Control block 152. The desired coolant temperature is input to Cooler/Heater Control block 156 along with the measured coolant temperature at block 160, and Cooler/Heater Control block 156 implements a PID control loop, for example, to adjust coolant temperature and stabilize the coolant at the appropriate temperature. The actual coolant temperature affects the temperature of the catheter and temperature to which prostate tissue and the rectum are elevated, which is represented by the line from Cooler/Heater Control block 156 to the tissue temperature elevation shown at block 142. Finally, as the rectal temperature returns to a value below the threshold, the catheter temperature modifier is reduced to zero, and the catheter temperature returns to the value provided by the catheter temperature profile at block 138, with the system stabilizing at the higher coolant temperature. By implementing this control method, rectal temperatures (and prostate tissue temperatures) reach the highest attainable level without exceeding a threshold rectal temperature, while simultaneously maintaining the catheter temperatu re set point at the maximum desired value consistent with patient comfort. It is somewhat counter-intuitive that coolant temperature should be increased in response to excessively high temperatures in the rectum, but it is nonetheless true where the catheter temperature is constrained to a predetermined steady-state value, since an increase in coolant temperature effectively forces a reduction in power provided to the microwave antenna to maintain the catheter at the steady-state value. The method of the present invention therefore enhances the effectiveness and reduces the necessary treatment time of the therapy.
The thermal therapy controlled by the method of the present invention must take into account the comfort level of the patient at various phases of the therapy. For example, the catheter temperature ramp rate or ramping function or the steady-state catheter temperature may potentially drive changes in power that may result in discomfort for the patient. Similarly, the coolant temperature ramp rate or ramping function or other parameters may also result in power level changes that could potentially cause some patient discomfort. As the thermal therapy session progresses, a physician may adjust the therapy at any time in response to an indication of patient discomfort, represented by block 158. Patient discomfort may potentially occur as a result of high absolute temperatures, or also as a result of high rates of change of temperatures, and therapy therefore is adjustable to change parameters related to both of these factors. The therapy parameter changes implemented by the physician (at blocks 130 and 132) are integrated into the therapy control method of the present invention to reduce or eliminate the discomfort of the patient.
FIG. 7B is a block diagram illustrating a complete thermal therapy control method according to a second embodiment of the present invention, utilizing the principles and parameters discussed above with respect to FIG. 6B. The majority of the method shown in FIG. 7B is identical to that shown in FIG. 7A, with one principal modification. Instead of utilizing a catheter temperature set point as shown in FIG. 7A, the modified method shown in FIG. 7B is concerned with a tissue temperature set point (that is, the temperature in tissue at some depth of interest from the catheter/urethra, defining a tissue protection zone). Therefore, to initialize the therapy, a physician enters an initial tissue temperature ramp rate/ramping function and a steady-state tissue temperature at block 130b, in a manner substantially similar to that described with respect to block 130a of FIG. 7A. From the tissue temperature inputs entered at block 130b, a tissue temperature profile is established at block 138b, which represents a desired characteristic of tissue temperature at a particular time in the thermal therapy session, which may of course be adjusted by other parameters such as rectal temperature and patient comfort during the course of the therapy, as noted below.
The tissue temperature profile signal is passed on to adder/subtractor 136, which passes a modified tissue temperature set point signal on to Microwave Power Control block 140, which is implemented as described above with respect to FIG. 7A. The power delivered to microwave antenna 30 (FIG. 2) energizes the antenna to radiate electromagnetic energy, resulting in elevation of prostate tissue as represented by block 142. Power delivered to the microwave antenna is continually adjusted to ensure that tissue at the depth of interest remains at the modified tissue temperature set point. In order to do so, Microwave Power Control block 140 must be responsive to tissue temperature. However, tissue temperature at a depth from the catheter/urethra typically cannot be measured directly without penetrating the urethra. Therefore, in one embodiment of the present invention, catheter temperature is measured at block 148, and tissue temperature is calculated at block 149 based on the measured catheter temperature (block 148), the microwave power level (block 140) and the measured coolant temperature (block 160). Microwave Power Control block 140 is therefore responsive to the calculated tissue temperature at block 149 to adjust microwave power accordingly. In an alternative embodiment, a temperature sensor may be positioned in the tissue by penetrating the urethra, or some other temperature sensing system for directly measuring tissue temperature may be implemented, in which case the measured tissue temperature would replace measured catheter temperature at block 148 of FIG. 7A, and there would be no need to calculate tissue temperature.
Rectal temperatures are also monitored during thermal therapy to ensure that the rectum is not thermally damaged by excessively high temperatures; the measured rectal temperature is represented by block 146. If rectal temperature reaches a predetermined threshold, steps must be taken to reduce the temperature of the rectum so that it may be preserved. As described above with respect to FIG. 7A, since coolant temperature may not be able to be instantaneously increased, the temperature set point is initially decreased to force microwave power to be immediately reduced. This tissue temperature set point is reduced by the tissue temperature modifier represented at block 150b, which is subtracted by adder/subtractor 136 from the desired tissue temperature to yield a modified tissue temperature set point input to Microwave Power Control block 140. As also described above with respect to FIG. 7A, after coolant temperature is increased and rectal temperature is returning to a value below the threshold, the tissue temperature modifier is reduced to zero, and the tissue temperature returns to the value provided by the tissue temperature profile at block 138b, with the system stabilizing at the higher coolant temperature.
FIG. 8A is a graph illustrating measured temperatures achieved during an actual thermal therapy treatment session in a clinical trial according to one variation of the control method of the present invention. In the clinical trial, anesthesia was used to ensure that the patients remained comfortable, so the patient comfort adaptability of the present invention was not utilized in the trial. Curve 180 represents the temperature of the catheter inserted into the urethra of the patient. Curve 182 represents the temperature of the coolant circulated between the antenna in the catheter and the urethral wall; the small oscillations in curve 182 are due to the heating/cooling system utilized in the trial. Curve 184 represents the microwave power level delivered to the antenna. Curve 188 represents the temperature of tissue at a depth of approximately 0.5 cm in the prostate surrounding the urethra.
Initially, power (curve 184) was ramped up quickly to raise the temperature of the catheter (curve 180) to approximately 40°C (the catheter temperature set point), with coolant temperature (curve 182) at an initial value of approximately 22°C. These characteristics correspond to the catheter temperature ramp rate and the initial coolant temperature set by the physician at blocks 130a and 132 (FIG. 7A). The ramp rate and ramping function may vary as described above; the clinical trial shown in FIG. 8A utilized a unit step function, which increased catheter temperature to the steady-state value as quickly as the system capabilities permitted. Coolant temperature was then reduced in step-wise increments, while the microwave power level was increased in turn to maintain the catheter temperature at the steady-state temperature such as 40°C (set by the physician in block 130a, FIG. 7A). The step-wise decrease in coolant temperature was set by the physician as the coolanttemperature ramp rate (block 132, FIG. 7A); again, the ramp rate and ramping function can vary as described above. As a result, the temperature of prostate tissue (curve 188) increased in a corresponding step-wise manner to the coolant temperature decrease. Coolant temperature finally reached a steady-state temperature, which again had been set by the physician at block 132, FIG. 7A. Also, throughout the therapy, rectal temperature was monitored to ensure that temperatures do not exceed a predetermined threshold, to prevent thermal damage to the rectum; no excessively high rectal temperatures were detected.
At a treatment time between 30 and 40 minutes, the catheter temperature set point (curve 180) was increased from 40°C to 42°C for experimental purposes. As expected, the increase in steady-state catheter temperature resulted in a corresponding increase in power (curve 184) and tissue temperature (curve 188), while the coolant temperature (curve 182) was kept constant.
Microwave power curve 184, catheter temperature curve 180 and tissue temperature curve 188 experience some oscillation at a treatment time between 40 and 50 minutes. These oscillations were due to a bladder spasm experienced by the patient at this time, which may occur from time to time during a thermal therapy treatment session. During the bladder spasm, although catheter temperature oscillated briefly, the control method of the present invention caused it to remain at a level approximately equal to or below the catheter temperature set point, and catheter temperature returned to the steady-state temperature automatically and stabilized with no outside intervention when the bladder spasm ceased.
FIG. 8B is a graph illustrating measured temperatures achieved during an actual thermal therapy treatment session in a clinical trial according to a second variation of the control method of the present invention. In the clinical trial, anesthesia was used to ensure that the patients remained comfortable, so the patient comfort adaptability of the present invention was not utilized in the trial. Curve 190 represents the temperature of the catheter inserted into the urethra of the patient. Curve 192 represents the temperature of the coolant circulated between the antenna in the catheter and the urethral wall. Curve 194 represents the microwave power level delivered to the antenna. Curve 198 represents the temperature of tissue at a depth of approximately 0.5 cm in the prostate surrounding the urethra.
Initially, power (curve 194) was ramped up quickly to raise the temperature of the catheter (curve 190) to approximately 40°C (the catheter temperature set point), with coolant temperature (curve 192) at an initial value of approximately 28°C. These characteristics correspond to the catheter temperature ramp rate and the initial coolant temperature set by the physician at blocks 130a and 132 (FIG. 7A). The ramp rate and ramping function may vary as described above; the clinical trial shown in FIG. 8B utilized a unit step function, which increased catheter temperature to the steady-state value as quickly as the system capabilities permitted. Coolant temperature was then reduced quickly, while the microwave power level was increased in turn to maintain the catheter temperature at the steady-state temperature such as 40°C (set by the physician in block 130a, FIG. 7A). The decrease in coolant temperature was set by the physician as the coolant temperature ramp rate (block 132, FIG. 7A); the function utilized was a unit step function causing coolant to decrease in temperature as quickly as the heating/cooling system would allow, but again, the ramp rate and ramping function can vary as described above. As a result, the temperature of prostate tissue (curve 188) increased in a manner corresponding to the coolant temperature decrease. Coolant temperature finally reached a steady-state temperature, which again had been set by the physician at block 132, FIG. 7A. Also, throughout the therapy, rectal temperature was monitored to ensure that temperatures do not exceed a predetermined threshold, to prevent thermal damage to the rectum; no excessively high rectal temperatures were detected. As can be seen in FIG. 8B, tissue temperatures exceeding about 90% of the peak tissue temperature were obtained within about 10 minutes.
It should be understood that the particular temperatures set and observed in the clinical trials illustrated by FIGS. 8A and 8B are exemplary, and the particular temperatures chosen and observed in practicing the present invention will vary depending on the patient's comfort level, the particular catheter structure utilized, and otherfactors.
The thermal therapy control method of the present invention is significant different from prior art control methods, in that the therapy is driven by controlling coolant temperature and making automatic corresponding adjustments to microwave power to maintain catheter or tissue temperature at a particular set point. In the absence of limiting parameters, coolant temperature is preferably as low as possible, so that microwave power is forced to correspondingly increase to maintain cathetertemperature constant and tissue is therefore heated to maximum temperatures. Rectal temperature is one factor that limits the therapy, since the rectum must be preserved below a threshold temperature to avoid thermal damage. The control method of the present invention allows the thermal therapy system to be optimally operated, with rectal temperatures as high as possible without thermally damaging the rectum and catheter temperatures maintained at a predetermined steady-state operating temperature. As a result, a precise depth of tissue necrosis is achievable with no physician intervention to control the therapy. Therapy times are also minimized, since the control method of the present invention allows tissue temperatures to reach 90% of their maximum value within about 10 minutes, if tolerable by the patient, which is a significant improvement over the prior art.
The thermal therapy control method of the present invention has been described primarily as it applies to treatment of a prostate from a urethra. However, the principles and methods of the present invention are likewise applicable to thermally treating other regions of tissue from adjacent body cavities. Preservation of adjacent organs may also be applicable, in a manner similar to the preservation of the rectum described above with respect to one preferred embodiment of the invention.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention.

Claims

A thermal therapy system comprising:
an applicator insertable into a urethra adjacent a targeted tissue region of prostate tissue, the applicator including a microwave antenna and at least one cooling fluid chamber for circulating a coolant between the microwave antenna and a wall of the urethra;

a rectal temperature sensing probe insertable into a rectum;

a microwave generator operable to energize the microwave antenna in the applicator;

a coolant temperature controller operable to control a
temperature of the coolant circulating between the microwave antenna and the wall of the urethra; and

a control system for selectively operating the microwave generator and the coolant temperature controller to decrease the temperature of the coolant to a steady-state coolant temperature, maintain selected tissue at a predetermined depth from the wall of the urethra at a temperature corresponding to a predetermined tissue temperature profile, characterized in that the control system is further configured for operating the microwave generator and the coolant temperature controller to increase the coolant temperature in response to detection of a predetermined rectal temperature profile so as to force a reduction in power provided by the microwave generator to the microwave antenna to maintain the selected tissue at a temperature corresponding to the predetermined tissue temperature profile.
The thermal therapy system of claim 1, further comprising means for permitting a physician to input the predetermined tissue temperature profile and the steady-state coolant temperature.
The thermal therapy system of claim 1, wherein the predetermined tissue temperature profile is a constant temperature of about 40°C.
The thermal therapy system of any of claims 1 to 3, further comprising means for permitting a physician to input a catheter temperature ramp rate, an initial coolant temperature and a coolant temperature ramp rate.
The thermal therapy system of any of claims 1 to 4, wherein the control system is operable to adjust at least one of the predetermined tissue temperature profile, the steady-state coolant temperature, the catheter temperature ramp rate, the initial coolant temperature and the coolant temperature ramp rate in response to patient comfort indicators.
The thermal therapy system of any of claims 1 to 5, wherein the control system is operable to temporarily decrease the temperature of the selected tissue from the predetermined tissue temperature profile upon detecting the predetermined rectal temperature profile.